2. Highly enantio- and diastereoselective Mannich reactions of glycine Schiff bases with in situ generated N-Boc-imines catalyzed by a cinchona alkaloid thiourea
Haile Zhang, Salahuddin Syed, Carlos F Barbas 3rd Org Lett. 2010 Feb 19;12(4):708-11. doi: 10.1021/ol902722y.
Highly enantio- and diastereoselective organocatalytic Mannich reactions of glycine Schiff bases with N-Boc-protected imines are described. Imines were generated in situ from bench-stable alpha-amido sulfones. Catalysis mediated by a cinchona alkaloid thiourea provided optically active alpha,beta-diamino acid derivatives with up to 99% ee and near-perfect diastereoselection.
3. A designer axially chiral amino sulfonamide as an efficient organocatalyst for direct asymmetric mannich reactions of N-Boc-protected imines
Taichi Kano, Yukako Yamaguchi, Keiji Maruoka Angew Chem Int Ed Engl. 2009;48(10):1838-40. doi: 10.1002/anie.200805628.
The moderate nucleophilicity of the axially chiral amino sulfonamide (S)-1 suppresses the problematic side reactions, including aldol reactions, in the asymmetric Mannich reaction of N-Boc-protected imines with aldehydes. The corresponding adducts are obtained in good yield and excellent stereoselectivity (see scheme; Boc = tert-butoxycarbonyl, Tf = trifluoromethanesulfonyl).